María-Luisa Marcos

Synthesis and electrochemical study of cobalt carbonyl complexes of trimethylsilyl-substituted 1,3,5-triethynylbenzene

Treatment of 1,3,5-tris(trimethylsilylethynyl)benzene or 1,3,5-triethynylbenzene with Co 2 (CO) 8 or Co 2 (CO) 6 (dppm) produced the formation of substituted ethynylcobalt complexes with one, two or three Co 2 (CO) 6 or Co 2 (CO) 4 (dppm) units, [{X 3 (Co 2 (CO) 6 )C 2 } n (XCC) m (1,3,5-C 6 H 3 )] (X=H or SiMe 3 ) ( n =1, 2 or 3; m =3− n ) and [{SiMe 3 (Co 2 (CO) 4 dppm)C 2 } n (SiMe 3 CC) m (1,3,5-C 6 H 3 )] ( n =1 or 2; m =3− n ), in a high yield. Desilylation of the non-metallated alkynes in [{SiMe 3 (Co 2 (CO) 4 dppm)C 2 }(SiMe 3 CC) 2 (1,3,5-C 6 H 3 )] occurred on treatment with KOH. Electrochemical results provide evidence for communication between the C 2 Co 2 centres. Crystals of [{SiMe 3 (Co 2 (CO) 4 dppm)C 2 } 2 (SiMe 3 CC)(1,3,5-C 6 H 3 )] suitable for single-crystal X-ray diffraction were grown and the molecular structure of this compound is discussed.

Alkynyl cobalt complexes. An electrochemical study

Abstract The preparation and characterisation of the complexes Co2(CO)5(PMe3)(μ-η2-Me3SiC2CCSiMe3) (2) and Co2(CO)4(PMe3)2(μ-η2-Me3SiC2CCSiMe3) (3) are described. A comparative electrochemical study of the complexes Co2(CO)6−nLn(μ-η2-Me3SiC2CCSiMe3) (n=0 (1); n=1, L=PMe3 (2); n=2, L=PMe3 (3), PPh2Me (4), dppa (5), dppm (6)) is presented by means of the cyclic and square-wave voltammetry techniques. Substitution of CO by phosphine ligands transforms the Co2C2 redox centre from a readily reducible to an easily oxidisable centre and contributes to the stabilisation of the Co–Co bond increasing the lifetime of the radical cations and anions.

Electrochemical study of methylfulvalene and methylcyclopentadiene molybdenum complexes

Abstract The product of the synthesis of ( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 ( 1 ) is reported as a mixture of six stereoisomers, the ratio of which has been unambigously assigned using homonuclear two dimensional correlation spectroscopy (COSY and NOESY). The reaction of Li 2 [( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 ] ( 2 ) with IMe yields ( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 Me 2 ( 3 ) and that of 1 with I 2 yields ( η 5 : η 5 -(C 5 H 3 Me) 2 )Mo 2 (CO) 6 I 2 ( 4 ). The electrochemical behaviour of 1 , 3 , and 4 is reported and compared with analogous complexes where other substituents are present on the fulvalene rings. Electronic communication through the fulvalene ligand seems to take place in 4 . The related compounds [( η 5 -C 5 H 4 R)Mo(CO) 3 ] 2 (R=Me ( 5 ), H ( 9 )), ( η 5 -C 5 H 4 R)Mo(CO) 3 Me (R=Me ( 7 ), H ( 10 )) and ( η 5 -C 5 H 4 R)Mo(CO) 3 I (R=Me ( 8 ), H ( 11 )) have been synthesized in order to compare their electrochemical behaviour with the fulvalene analogous.

[Co4(CO)12] derivatives with bis(diphenylphosphino) amine, an electrochemical study

Abstract [CO 4 (CO) 12 ] ( A ) reacts with bis(diphenylphosphino)amine (dppa) to give [Co 4 (CO) 10 (dppa)] ( B ) or [Co 4 (CO) 8 (dppa) 2 ] ( C ) when the reactant ratios are 1:1 or 1:2, respectively. The complexes have been characterized by elemental analysis, IR, 1 H and 31 P NMR spectroscopy. The electrochemical behaviour of the three compounds has been studied. The reduction voltammetric waves and the first oxidation of C are reversible, although other waves were also observed which were attributed to the fragmentation induced by electron transfer. Using the electrochemical and UV-visible data, it was possible to construct MO diagrams and to locate the HOMO, LUMO and other MOs of the metal core.

Stabilization of 17-electron metal-centered species. Electrochemical study of [WX(CO)3(η5-C5H5)] (X=Cl, Br, I) and [WI(CO)2(PCy3)(η5-C5H5)]

The electrochemical study of [WX(CO)3(η5-C5H5)] (X=Cl, Br, I) (1–3) is reported. The reductions follow ECE mechanisms, yielding the anion [W(CO)3(η5-C5H5)]− (7−). The stability of 1–3 towards reduction increases with the increasing electronegativity and decreasing size of the halide. 7− reoxidizes to the unstable 17-electron radical [W(CO)3(η5-C5H5)] (7), which readily dimerizes. The oxidations of 1–3 follow EC mechanisms, leading to the cations [WX(CO)3(η5-C5H5)]+, which are very unstable and readily decompose. [WI(CO)2(PCy3)(η5-C5H5)] has been prepared and characterized as a mixture of cis (4) and trans (5) isomers (ratio cis:trans 95:5). The electrochemical reduction of the cis isomer (4) is also an ECE process, but takes place at a potential significantly more negative than 3. An anion [W(CO)2(PCy3)(η5-C5H5)]− (8−) is formed which reoxidizes to 8. This new 17-electron radical is considerably more stable than 7 due to the presence of the bulky PCy3 ligand. A similar effect is observed in the oxidation of 4, where the 17-electron product 4+ is significantly more stable than the analogue 3+.